Democrats are alleging foreign money is being used to influence this year's Midterm Elections. The vote is just three weeks away, and the floodgates of cash being spent to try to sway voters are open.

The US Chamber of Commerce, the nation's largest business lobby group, has vowed to spend $75m on winning races in key states. Most of the money they're spending is for Republican candidates. But they don't have to disclose their sources of funding.

In January, US Supreme Court decided in the Citizens United case that government can't regulate political speech, with money being defined as an element of political speech.

Now the White House is using the much criticized High Court decision as an election tool. At a rally in Philadelphia on Sunday, Obama said foreign money could be used by Republicans to influence voters, "You don’t know. It could be the oil industry. It could be the insurance industry. It could even be foreign-owned corporations. You don’t know because they don’t have to disclose. Now, that's not just a threat to Democrats - that's a threat to our democracy."

And top Obama adviser David Axelrod reiterated the attack, calling on the Chamber to release its list of donors to prove they're not using foreign money to buy ads.

Democratic supporters have gone on to accuse the Republicans of being influenced by foreign companies that send jobs overseas. It's a very sensitive issue in the US with high unemployment and years of outsourcing. A new ad running in Illinois by a Democratic interest group accuses the Chamber of taking money from corporations in places like China and India, "the same companies that threaten American jobs."

But neither Obama nor his aides nor the ads point to any specific foreign company. They might say they can't provide any evidence because there is no disclosure.

The Chamber of Commerce has denied spending foreign money on political ads."The Chamber is careful to ensure we comply with all applicable laws and no foreign money is used to fund political activities." But their donor list remains locked up.

Top Republicans have hit back against the Democratic attack. Former Republican National Committee chairman Ed Gillespie said on Sunday, "Don't accuse those who are playing by the rules of somehow doing something that is unethical or illegal."

Efforts to mandate disclosure of campaign funding have so far failed this year in Congress. As the airwaves become even more saturated with political ads ahead of the November 2nd vote, the implications of the Supreme Court decision and its use as a political weapon continue in a circle of accusation and denial with neither side providing proof.